Systems of Bonded Substrates and Methods for Bonding Substrates with Bonding Layers

ABSTRACT

A system of bonded substrates may include a first substrate, a second substrate, and a bonding layer. The first substrate may include a bonding surface, wherein a geometry of the bonding surface of the first substrate includes a plurality of microchannels. The second substrate may include a complementary bonding surface. The bonding layer may be positioned between the first substrate and the second substrate, wherein the bonding layer may fill the microchannels of the first substrate and may contact substantially the entire bonding surface of the first substrate. The bonding layer may include a metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of and claimspriority to U.S. patent application Ser. No. 14/794,315 filed Jul. 8,2015 and entitled “Systems of Bonded Substrates and Methods for BondingSubstrates with Bonding Layers,” which is incorporated by referenceherein.

TECHNICAL FIELD

The present specification generally relates to the bonding of substratesand, more specifically, to the bonding of substrates exposed to thermalcycling.

BACKGROUND

Components of electrical devices which operate at elevated temperaturesmay need to be bonded with one another. For example, power semiconductordevices, such as those fabricated from silicon carbide, may be designedto operate at very high operating temperatures (e.g., greater than 250°C.). Such power semiconductor devices may be bonded to a cooling device,such as heat sink or a liquid cooling assembly. The cooling deviceremoves heat from the power semiconductor to ensure that it operates ata temperature that is below its maximum operating temperature. Thebonding layer that bonds the power semiconductor device to the coolingdevice must be able to withstand the high operating temperatures of thepower semiconductor device. However, conventional bonding techniques maybe difficult and/or costly, and may not have sufficient bond strengthover thermal cycling. For example, prolonged heating times for bondingand the use of wetting agents on the substrates may by be requiredaccording to conventional bonding techniques.

Accordingly, a need exists for alternative methods for bonding twosubstrates to one another.

SUMMARY

In one embodiment, a first substrate may be bonded to a second substratein a method that may comprise providing the first substrate, providing asecond substrate, providing a bonding layer precursor, positioning thebonding layer precursor between the first substrate and the secondsubstrate, and bonding the first substrate to the second substrate byheating the bonding layer precursor to form a bonding layer. The firstsubstrate may comprise a bonding surface, and a geometry of the bondingsurface of the first substrate may comprise a plurality ofmicrochannels. The second substrate may comprise a complementary bondingsurface and the bonding layer precursor may comprise a metal. The firstsurface of the bonding layer precursor may be in contact with at least aportion of the bonding surface of the first substrate, and the secondsurface of the bonding layer precursor may be in contact with at least aportion of the bonding surface of the second substrate. The bondinglayer may fill the microchannels of the first substrate and may contactsubstantially the entire bonding surface of the first substrate.

In another embodiment, a system of bonded substrates may comprise afirst substrate, a second substrate, and a bonding layer. The firstsubstrate may comprise a bonding surface, wherein a geometry of thebonding surface of the first substrate may comprise a plurality ofmicrochannels. The second substrate may comprise a complementary bondingsurface. The bonding layer may be positioned between the first substrateand the second substrate, wherein the bonding layer may fill themicrochannels of the first substrate and may contact substantially theentire bonding surface of the first substrate. The bonding layer maycomprise a metal.

In yet another embodiment, a first substrate may be bonded to a secondsubstrate in a method that may comprise providing the first substrate,providing a second substrate, providing a bonding layer precursor,positioning the bonding layer precursor between the first substrate andthe second substrate, and bonding the first substrate to the secondsubstrate by heating the bonding layer precursor to form a bondinglayer. The first substrate may comprise a bonding surface, wherein ageometry of the bonding surface of the first substrate may comprise aplurality of microchannels having a depth from about 5 microns to about10 microns. A material of the first substrate at the bonding surface maybe chosen from aluminum, copper, nickel, or combinations thereof. Thesecond substrate may comprise a complementary bonding surface, wherein ageometry of the bonding surface of the second substrate may comprise aplurality of microchannels having a depth from about 5 microns to about10 microns. A material of the second substrate at the bonding surfacemay be chosen from aluminum, copper, nickel, or combinations thereof.The bonding layer precursor may be substantially planar and may comprisea first surface and a second surface, the distance between the firstsurface and second surface defining a thickness of the bonding layerprecursor. The bonding layer precursor may comprise tin. The bondinglayer precursor may be positioned between the first substrate and thesecond substrate, wherein the first surface of the bonding layerprecursor may be in contact with at least a portion of the bondingsurface of the first substrate, and the second surface of the bondinglayer precursor may be in contact with at least a portion of the bondingsurface of the second substrate. The bonding layer may fill themicrochannels of the first substrate and the microchannels of the secondsubstrate. The bonding layer may contact substantially the entirebonding surface of the first substrate and substantially the entirebonding surface of the second substrate.

These and additional features provided by the embodiments describedherein will be more fully understood in view of the following detaileddescription, in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments set forth in the drawings are illustrative and exemplaryin nature and not intended to limit the subject matter defined by theclaims. The following detailed description of the illustrativeembodiments can be understood when read in conjunction with thefollowing drawings, where like structure is indicated with likereference numerals and in which:

FIG. 1 schematically depicts a cross-sectional side view of twosubstrates and a bonding layer in a pre-bonded state, according to oneor more embodiments shown and described herein;

FIG. 2 schematically depicts a cross-sectional side view of twosubstrates bonded to one another with a bonding layer, according to oneor more embodiments shown and described herein;

FIG. 3 schematically depicts a perspective view of a substrate,according to one or more embodiments shown and described herein;

FIG. 4 schematically depicts a cross-sectional side view of a substratebonding surface comprising microchannels with rectangular cross-section,according to one or more embodiments shown and described herein;

FIG. 5 schematically depicts a cross-sectional side view of a substratebonding surface comprising microchannels with curved cross-section,according to one or more embodiments shown and described herein;

FIG. 6 schematically depicts a cross-sectional side view of a substratebonding surface comprising microchannels with pentagonal cross-section,according to one or more embodiments shown and described herein;

FIG. 7A schematically depicts a top view of a substrate bonding surfacecomprising linearly arranged parallel microchannels 490, according toone or more embodiments shown and described herein;

FIG. 7B schematically depicts a top view of a substrate bonding surfacecomprising crisscrossing linear microchannels 490, according to one ormore embodiments shown and described herein;

FIG. 7C schematically depicts a top view of a substrate bonding surfacecomprising circularly arranged microchannels 490, according to one ormore embodiments shown and described herein; and

FIG. 8 schematically depicts a cross-sectional side view of twosubstrates bonded to one another with a bonding layer, according to oneor more embodiments shown and described herein.

DETAILED DESCRIPTION

Referring generally to the figures, embodiments of the presentdisclosure are directed to methods for bonding two or more substratestogether with a thermally conductive bonding layer, and additionally, tothe resulting bonded substrates. Generally, each of the substrates maycomprise a substrate bonding surface which contacts a bonding layer thatis positioned between and contacting the substrates. One or both of thesubstrate bonding surfaces may comprise a plurality of microchannelswhich may improve bonding strength and/or durability of the bond. Duringa bonding process, which may involve heating of at least a bonding layerprecursor, the microchannels may promote capillary action between thesolid substrates and the melted bonding layer precursor. Variousembodiments of bonded substrate systems and methods for bondingsubstrates are described in detail herein.

FIG. 1 generally depicts one embodiment of an upper substrate 200, alower substrate 400, and a bonding layer precursor 301, such as ametallic foil, in a pre-bonded state. FIG. 2 generally depicts a systemof bonded substrates 100 comprising an upper substrate 200 and a lowersubstrate 400 bonded to one another with a bonding layer 300 that isformed by heating of the bonding layer precursor 301. The bonding layer300 is positioned generally between the upper substrate 200 and thelower substrate 400 and directly contacting the upper substrate 200 andlower substrate 400. While one substrate is referred to herein as the“upper substrate” and the other substrate is referred to herein as the“lower substrate,” the two substrates need not necessarily be arrangedabove and below one another, and the nomenclature of “upper” and “lower”is merely representative of the relative positioning in the uppersubstrate 200 and lower substrate 400 as depicted in the drawingsdescribed herein. Additionally, it should be understood herein that anyfeature of the upper substrate 200 may be included in the lowersubstrate 400, and vice versa. Generally, the lower substrate 400 andthe upper substrate 200 each comprise bonding surfaces, referred to asthe lower substrate bonding surface 402 and upper substrate bondingsurface 202, respectively. The lower substrate bonding surface 402 andupper substrate bonding surface 202 may be referred to as“complementary” herein, meaning that the two bonding surfaces generallyhave geometries making them suitable for bonding with one another, suchas with a bonding layer 300 as described in embodiments herein.

In one embodiment, the lower substrate 400 may comprise a lowersubstrate body 420 and a lower substrate surface member 410. The lowersubstrate surface member 410 may be positioned on a surface of the lowersubstrate body 420 and may comprise a lower substrate bonding surface402. In one embodiment, the lower substrate bonding surface 402 may besubstantially planar and may generally comprise a plurality ofmicrochannels 490.

The lower substrate body 420 may comprise a wide variety of materials,including, but not limited to, metals such as copper, aluminum, nickel,or combinations thereof. In embodiments, the lower substrate body 420may comprise at least about 50 wt % copper, at least about 60 wt %copper, at least about 70 wt % copper, at least about 80 wt % copper, atleast about 90 wt % copper, at least about 95 wt % copper, at leastabout 99 wt % copper, at least about 99.5 wt % copper, at least about 50wt % aluminum, at least about 60 wt % aluminum, at least about 70 wt %aluminum, at least about 80 wt % aluminum, at least about 90 wt %aluminum, at least about 95 wt % aluminum, at least about 99 wt %aluminum, at least about 99.5 wt % aluminum, at least about 50 wt %nickel, at least about 60 wt % nickel, at least about 70 wt % nickel, atleast about 80 wt % nickel, at least about 90 wt % nickel, at leastabout 95 wt % nickel, at least about 99 wt % nickel, and/or at leastabout 99.5 wt % nickel. For example, the lower substrate body 420 maycomprise a heat sink for a power electronic device. In otherembodiments, the lower substrate body 420 may comprise non-metals suchas, but not limited to, metal oxides, metal nitrides, metal carbides, orcombinations thereof, including, but not limited to, alumina, berylliumoxide, aluminum nitride, silicon carbide, or combinations thereof. Forexample, the lower substrate body 420 may comprise a die for a powerelectronic device. In embodiments, the lower substrate body 420 maycomprise at least about 50 wt % metal oxides, at least about 60 wt %metal oxides, at least about 70 wt % metal oxides, at least about 80 wt% metal oxides, at least about 90 wt % metal oxides, at least about 95wt % metal oxides, at least about 99 wt % metal oxides, at least about99.5 wt % metal oxides, at least about 50 wt % metal nitrides, at leastabout 60 wt % metal nitrides, at least about 70 wt % metal nitrides, atleast about 80 wt % metal nitrides, at least about 90 wt % metalnitrides, at least about 95 wt % metal nitrides, at least about 99 wt %metal nitrides, at least about 99.5 wt % metal nitrides, at least about50 wt % metal carbides, at least about 60 wt % metal carbides, at leastabout 70 wt % metal carbides, at least about 80 wt % metal carbides, atleast about 90 wt % metal carbides, at least about 95 wt % metalcarbides, at least about 99 wt % metal carbides, and/or at least about99.5 wt % metal carbides.

The lower substrate surface member 410 is generally attached to thelower substrate body 420 and comprises a lower substrate bonding surface402. The lower substrate bonding surface 402 comprises a plurality ofmicrochannels 490. The microchannels 490 may be formed in the surface ofthe lower substrate bonding surface 402, as shown in FIG. 3. In oneembodiment, the lower substrate surface member 410 may comprise one ormore metals such as, but not limited to, copper, aluminum, nickel, orcombinations thereof. In embodiments, the lower substrate surface member410 may comprise at least about 50 wt % copper, at least about 60 wt %copper, at least about 70 wt % copper, at least about 80 wt % copper, atleast about 90 wt % copper, at least about 95 wt % copper, at leastabout 99 wt % copper, at least about 99.5 wt % copper, at least about 50wt % aluminum, at least about 60 wt % aluminum, at least about 70 wt %aluminum, at least about 80 wt % aluminum, at least about 90 wt %aluminum, at least about 95 wt % aluminum, at least about 99 wt %aluminum, at least about 99.5 wt % aluminum, at least about 50 wt %nickel, at least about 60 wt % nickel, at least about 70 wt % nickel, atleast about 80 wt % nickel, at least about 90 wt % nickel, at leastabout 95 wt % nickel, at least about 99 wt % nickel, and/or at leastabout 99.5 wt % nickel. The composition of the lower substrate surfacemember 410 at the lower substrate bonding surface 402 may be any of thematerial compositions disclosed herein.

The geometry of the lower substrate bonding surface 402 generallycomprises a plurality of microchannels 490. In one embodiment, themicrochannels 490 may generally comprise a length component, a widthcomponent, and a depth component. Referring to FIG. 3, in oneembodiment, the microchannels 490 may generally comprise a lengthcomponent in the y-coordinate direction, a width component in thex-coordinate direction, and a depth component in the z-coordinatedirection. The microchannels 490 may generally be positioned along thelower substrate bonding surface 402, such as linearly arranged in oneembodiment, where the length of the lower substrate bonding surface 402is substantially parallel to the lower substrate bonding surface 402.

FIG. 4 depicts and enlarged cross-sectional view of the microchannels490 of the embodiment of FIG. 1. The microchannels 490 have amicrochannel height 460 and a microchannel width 450. As used herein,the microchannel height 460 is measured from the deepest part of themicrochannels 490 and the microchannel width 450 is measured as thegreatest distance between sides of microchannels 490.

The length of each microchannel 490 may be greater than or equal toabout 1 micron, 5 microns, 50 microns, 100 microns, 500 microns, 1000microns, 5 mm, 10 mm or even greater than about 20 mm. In embodiments,the length of each microchannel 490 may be from about 1 micron to about50 mm, from about 3 microns to about 20 mm, from about 50 microns toabout 15 mm, from about 200 microns to about 15 mm, or from about 1000microns to about 12 mm. The depth of the microchannels 490 may begreater than about 1 micron, greater than about 2 microns, greater thanabout 5 microns, greater than about 10 microns, greater than about 20microns, or even greater than about 50 microns. In embodiments, thedepth of the microchannels 490 may be from about 1 micron to about 50microns, from about 5 microns to about 50 microns, from about 2 micronsto about 25 microns, from about 3 microns to about 15 microns, or fromabout 5 microns to about 10 microns. The width of the microchannels 490may be greater than about 1 micron, greater than about 2 microns,greater than about 5 microns, greater than about 10 microns, greaterthan about 20 microns, or even greater than about 50 microns. Inembodiments, the width of the microchannels 490 may be from about 1micron to about 50 microns, from about 2 microns to about 25 microns,from about 3 microns to about 15 microns, or from about 5 microns toabout 10 microns. The ratio of the length to the depth of eachmicrochannels 490 may be at least about 5:1, at least about 10:1, atleast about 15:1, at least about 20:1, at least about 50:1, at leastabout 100:1, or even at least about 250:1. The microchannels 490 maycomprise a microchannel spacing 470 defined by the distance betweenadjacent microchannels 490. The average microchannel spacing is definedby the average distance between adjacent microchannels 490. The averagemicrochannel spacing may be from about be from about 1 micron to about50 microns, from about 2 microns to about 25 microns, from about 3microns to about 15 microns, or from about 5 microns to about 10microns.

In embodiments, the microchannels 490 may have a wide variety ofcross-sectional shapes. For example, FIG. 4 depicts substantiallyrectangular-shaped microchannels 490, FIG. 5 depicts substantiallycurved-shaped microchannels 490, and FIG. 6 depicts substantiallypentagonal-shaped microchannels 490. It should be understood that themicrochannels 490 may have substantially any shaped cross section.Additionally, as shown in FIGS. 7A, 7B, and 7C, the microchannels 490may comprise a variety of patterns on the lower substrate bondingsurface 402. For example, FIG. 7A depicts a pattern with substantiallystraight microchannels 490 that are substantially parallel relative toone another, FIG. 7B depicts a pattern with substantially straightmicrochannels 490 that crisscross at about a 90° angle (other angles ofintersection are contemplated herein), and FIG. 7C depicts a patternwith substantially circular microchannels 490 that form a “bull-eye”configuration.

The lower substrate surface member 410 comprises a thickness 430 whichis measured as the maximum thickness of the lower substrate surfacemember 410 in the direction substantially perpendicular to the planarlower substrate bonding surface 402 from the lower substrate body 420 tothe bonding layer 300. The thickness 430 may at least about 5 microns,at least about 10 microns, at least about 20 microns, at least about 50microns, at least about 100 microns, or at even at least about 200microns. In additional embodiments, the thickness 430 may be less thanabout 200 microns, less than about 100 microns, less than about 50microns, less than about 20 microns, less than about 10 microns, or evenless than about 5 microns. In embodiments, the thickness 430 may be fromabout 10 microns to about 100 microns, from about 10 microns to about300 microns, or from about 5 microns to about 400 microns. The lowersubstrate surface member 410 comprises a thickness 440 which is measuredas the minimum thickness of the lower substrate surface member 410 inthe direction substantially perpendicular to the planar lower substratebonding surface 402 from the lower substrate body 420 to the bondinglayer 300 (i.e., at the bottom of the microchannels 490. The thickness440 may at least about 5 microns, at least about 10 microns, at leastabout 20 microns, at least about 50 microns, at least about 100 microns,or at even at least about 200 microns. In additional embodiments, thethickness 440 may be less than about 200 microns, less than about 100microns, less than about 50 microns, less than about 20 microns, lessthan about 10 microns, or even less than about 5 microns. Inembodiments, the thickness 430 may be from about 10 microns to about 100microns, from about 10 microns to about 300 microns, or from about 5microns to about 400 microns.

In one embodiment, the lower substrate surface member 410 may comprise adirect bonded metal, such as, but not limited to, direct bonded copper(DBC) or direct bonded aluminum (DBA). For example, direct bondedmetallic layer may be bonded to the lower substrate body 420 by ahigh-temperature oxidation process where the copper and the lowersubstrate body 420 are heated to a controlled temperature in anatmosphere of nitrogen containing about 30 ppm of oxygen to form acopper-oxygen eutectic. In one embodiment, the microchannels 490 may beformed by an etching process. Any suitable etching process may beemployed, such as acid chemical etching or laser etching. Themicrochannel patterns, such as those depicted in FIGS. 7A, 7B, and 7Cmay be etched with appropriately patterned etching masks. In anotherembodiment, the lower substrate surface member 410 may comprise amaterial that is metal plated on the lower substrate bonding surface402, such as a nickel plated lower substrate bonding surface 402.

In another embodiment, the lower substrate surface member 410 maycomprise pores which act as microchannels. The lower substrate surfacemember 410 may comprise a material having a porous structure comprisingpores with average pore size of from about 1 micron to about 20 microns,from about 3 microns to about 15 microns, or from about 5 microns toabout 10 microns. The lower substrate surface member 410 may have fromabout 30% porosity to about 70% porosity, or from about 40% to about 60%porosity.

The upper substrate 200 may comprise an upper substrate body 220 and anupper substrate surface member 210. The upper substrate surface member210 may be positioned on a surface of the upper substrate body 220 andmay comprise an upper substrate bonding surface 202. In one embodiment,the upper substrate body 220 may be substantially planar and maygenerally comprise a plurality of microchannels 290.

The upper substrate body 220 may comprise a wide variety of materials,including, but not limited to, metals such as copper, aluminum, nickel,and combinations thereof. In embodiments, the upper substrate body 220may comprise at least about 50 wt % copper, at least about 60 wt %copper, at least about 70 wt % copper, at least about 80 wt % copper, atleast about 90 wt % copper, at least about 95 wt % copper, at leastabout 99 wt % copper, at least about 99.5 wt % copper, at least about 50wt % aluminum, at least about 60 wt % aluminum, at least about 70 wt %aluminum, at least about 80 wt % aluminum, at least about 90 wt %aluminum, at least about 95 wt % aluminum, at least about 99 wt %aluminum, at least about 99.5 wt % aluminum, at least about 50 wt %nickel, at least about 60 wt % nickel, at least about 70 wt % nickel, atleast about 80 wt % nickel, at least about 90 wt % nickel, at leastabout 95 wt % nickel, at least about 99 wt % nickel, and/or at leastabout 99.5 wt % nickel. For example, the upper substrate body 220 maycomprise a heat sink for a power electronic device. In otherembodiments, the upper substrate body 220 may comprise non-metalmaterial such as, but not limited to, metal oxides, metal nitrides,metal carbides, or combinations thereof, including, but not limited to,alumina, beryllium oxide, aluminum nitride, silicon carbide, orcombinations thereof. For example, the upper substrate body 220 maycomprise a die for a power electronic device. In embodiments, the uppersubstrate body 220 may comprise at least about 50 wt % metal oxides, atleast about 60 wt % metal oxides, at least about 70 wt % metal oxides,at least about 80 wt % metal oxides, at least about 90 wt % metaloxides, at least about 95 wt % metal oxides, at least about 99 wt %metal oxides, at least about 99.5 wt % metal oxides, at least about 50wt % metal nitrides, at least about 60 wt % metal nitrides, at leastabout 70 wt % metal nitrides, at least about 80 wt % metal nitrides, atleast about 90 wt % metal nitrides, at least about 95 wt % metalnitrides, at least about 99 wt % metal nitrides, at least about 99.5 wt% metal nitrides, at least about 50 wt % metal carbides, at least about60 wt % metal carbides, at least about 70 wt % metal carbides, at leastabout 80 wt % metal carbides, at least about 90 wt % metal carbides, atleast about 95 wt % metal carbides, at least about 99 wt % metalcarbides, and/or at least about 99.5 wt % metal carbides.

The upper substrate surface member 210 is generally attached to theupper substrate body 220 and comprises an upper substrate bondingsurface 202. The upper substrate bonding surface 202 comprises aplurality of microchannels 290. The microchannels 290 may be formed inthe upper substrate bonding surface 202 of the upper substrate surfacemember 210, similar to as shown in FIG. 3. In one embodiment, the uppersubstrate surface member 210 may comprise one or more metals such as,but not limited to, copper, aluminum, nickel, or combinations thereof.In embodiments, the upper substrate surface member 210 may comprise atleast about 50 wt % copper, at least about 60 wt % copper, at leastabout 70 wt % copper, at least about 80 wt % copper, at least about 90wt % copper, at least about 95 wt % copper, at least about 99 wt %copper, at least about 99.5 wt % copper, at least about 50 wt %aluminum, at least about 60 wt % aluminum, at least about 70 wt %aluminum, at least about 80 wt % aluminum, at least about 90 wt %aluminum, at least about 95 wt % aluminum, at least about 99 wt %aluminum, at least about 99.5 wt % aluminum, at least about 50 wt %nickel, at least about 60 wt % nickel, at least about 70 wt % nickel, atleast about 80 wt % nickel, at least about 90 wt % nickel, at leastabout 95 wt % nickel, at least about 99 wt % nickel, and/or at leastabout 99.5 wt % nickel.

It should be understood that an aspect of the lower substrate 400disclosed herein may be included in the upper substrate 200. Forexample, the characteristics of the microchannels 490 disclosed in FIGS.3, 4, 5, 6, 7A, 7B, and 7C may be included in the upper substrate 200.The structures and accompanying description of FIGS. 3, 4, 5, 6, 7A, 7B,and 7C is equally applicable to the upper substrate 200 and lowersubstrate 400. Additionally, it should be understood the upper substrate200, the lower substrate 400, or both, may include microchannels.

The upper substrate surface member 210 comprises a thickness 230 whichis measured as the maximum thickness of the upper substrate surfacemember 210 in the direction substantially perpendicular to the planarupper substrate bonding surface 202. The thickness 230 may at leastabout 5 microns, at least about 10 microns, at least about 20 microns,at least about 50 microns, at least about 100 microns, or at even atleast about 200 microns. In additional embodiments, the thickness 230may be less than about 200 microns, less than about 100 microns, lessthan about 50 microns, less than about 20 microns, less than about 10microns, or even less than about 5 microns. In embodiments, thethickness 230 may be from about 10 microns to about 100 microns, fromabout 10 microns to about 300 microns, or from about 5 microns to about400 microns. The upper substrate surface member 210 comprises athickness 240 which is measured as the minimum thickness of the uppersubstrate surface member 210 in the direction substantiallyperpendicular to the planar upper substrate bonding surface 202 from theupper substrate body 220 to the bonding layer 300 (i.e., at the bottomof the microchannels 290. The thickness 240 may at least about 5microns, at least about 10 microns, at least about 20 microns, at leastabout 50 microns, at least about 100 microns, or at even at least about200 microns. In additional embodiments, the thickness 240 may be lessthan about 200 microns, less than about 100 microns, less than about 50microns, less than about 20 microns, less than about 10 microns, or evenless than about 5 microns. In embodiments, the thickness 240 may be fromabout 10 microns to about 100 microns, from about 10 microns to about300 microns, or from about 5 microns to about 400 microns.

In one embodiment, the upper substrate surface member 210 may comprise adirect bonded metal, such as, but not limited to, direct bonded copper(DBC) or direct bonded aluminum (DBA). For example, direct bondedmetallic layer may be bonded to the upper substrate body 220 by ahigh-temperature oxidation process where the copper or aluminum and theupper substrate body 220 are heated to a controlled temperature in anatmosphere of nitrogen containing about 30 ppm of oxygen to form acopper-oxygen eutectic. In one embodiment, the microchannels 290 may beformed by an etching process. Any suitable etching process may beemployed, such as acid chemical etching or laser etching. Themicrochannel patterns, such as those depicted in FIGS. 7A, 7B, and 7Cmay be etched with appropriately patterned etching masks. In anotherembodiment, the upper substrate surface member 210 may comprise amaterial that is metal plated on the upper substrate bonding surface202, such as a nickel plated upper substrate bonding surface 202.

In another embodiment, the upper substrate surface member 210 maycomprise pores which act as microchannels. The upper substrate surfacemember 210 may comprise a material having a porous structure comprisingpores with average pore size of from about 1 micron to about 20 microns,from about 3 microns to about 15 microns, or from about 5 microns toabout 10 microns. The upper substrate surface member 210 may have fromabout 30% porosity to about 70% porosity, or from about 40% to about 60%porosity.

As shown in FIG. 1, prior to bonding, a bonding layer precursor 301 ispositioned between the upper substrate 200 and the lower substrate 400.The bonding layer precursor 301 may comprise a first surface 306 and asecond surface 308, where the distance between the first surface 306 andsecond surface 308 defines a thickness 304 of the bonding layerprecursor 301. The bonding layer precursor 301 may be substantiallyplanar. In one embodiment, the bonding layer precursor 301 is a solidmetallic foil. The thickness 304 of the bonding layer precursor 301 maybe from about 5 microns to about 100 microns, from about 10 microns toabout 50 microns, or from about 15 microns to about 30 microns. In oneembodiment, the bonding layer precursor 301 may comprise tin, such as atleast about at least about 50 wt % tin, at least about 60 wt % tin, atleast about 70 wt % tin, at least about 80 wt % tin, at least about 90wt % tin, at least about 95 wt % tin, at least about 99 wt % tin.

Referring now to FIGS. 1 and 2, through a heating process, the bondinglayer precursor 301 becomes the bonding layer 300. The bonding layer 300bonds the upper substrate 200 with the lower substrate 400. The bondinglayer 300 may securely attach the lower substrate 400 to the uppersubstrate 200. As such, the bonding layer precursor 301 may generallycomprise the same composition as the bonding layer 300, and thematerials of the bonding layer precursor 301 and bonding layer 300(excluding the materials formed at the bonding interface byinter-metallic bonding, e.g., materials of a formed eutectic systems)may be interchangeably used herein. The heat treatment may be at atemperature of at least about the melting point of the material of thebonding layer precursor 301, but may be at a temperature below themelting point of the material of the upper substrate 200 and lowersubstrate 400. The materials of the upper substrate 200 and lowersubstrate 400 may generally have a higher melting point than thematerial of the bonding layer 300. Upon heating, the bonding layerprecursor 301 melts to form the bonding layer 300, where the bondinglayer 300 fills the microchannels 290 of the upper substrate bondingsurface 202 and the microchannels 490 of the lower substrate bondingsurface 402. By substantially filling the microchannels 290, 490, thebonding layer 300 may contact substantially the entire upper substratebonding surface 202 and/or lower substrate bonding surface 402. As shownin FIG. 1, empty area 310 in the microchannels 290, 4290 is filled withthe bonding layer 300 in FIG. 2. Without being bound by theory, it isbelieved that bonding is improved between the bonding layer 300 and theupper substrate 200 and/or lower substrate 400 by capillary actioncaused by the microchannels 290, 490. In general, capillary action(sometimes referred to as capillarity, capillary motion, or wicking) isthe ability of a liquid to flow in narrow spaces without the assistanceof, and in opposition to, external forces like gravity. It occursbecause of intermolecular forces between the liquid and surroundingsolid surfaces. The geometry of the microchannels 290, 490 may allow forcapillary action between the melted material of the bonding layer 300and the edges of the microchannels 290, 490.

In another embodiment, the bonding layer precursor 301 may comprise aplurality of metal particles in a binder matrix. The metal particles maybe from about 1 micron to about 100 microns in diameter, and may besubstantially spherical in shape. The binder may be a polymer binderwhich burns out of the bonding layer precursor 301 when heated to meltthe metal particles. The metal particles may comprise tin.

In some embodiments, the materials of the upper substrate 200 and/orlower substrate 400 may have melting points of at least about 300° C.,at least about 400° C., at least about 500° C., at least about 600° C.,at least about 800° C., or even at least about 1000° C. The material ofthe bonding layer 300 may have a melting point of less than about 300°C., less than about 275° C., less than about 250° C., or even less thanabout 240° C. For example, in a system with a tin bonding layer 300 andcopper upper substrate surface member 210 and lower substrate surfacemember 410, the tin may have a melting point of about 232° C. and thecopper may have a melting point of about 1085° C. In such an embodiment,the heat treatment for bonding may be greater than about 250° C. butless than about 1000° C., such as from about 250° C. to about 300° C.The heating time may be any suitable time for melting of the bondinglayer precursor 301, such as about 15 minutes to about several hours.The heating may be in a vacuum environment or in air. In embodiments,the material or materials of the upper substrate 200 and/or lowersubstrate 400 may have a melting point that is greater than the meltingpoint of one or more components of the bonding layer 300. For example,the material or materials of the upper substrate 200 and/or lowersubstrate 400 may have a melting point of at least about 50° C. greater,at least about 100° C. greater, at least about 200° C. greater, or evenat least about 400° C. greater than the material of the bonding layer300.

In one embodiment, no wetting agent is needed for bonding of the bondinglayer 300 to the upper substrate 200 and/or lower substrate 400. Awetting agent may be employed in conventional bonding techniques.However, without being bound by theory, it is believed that themicrochannels 290, 490 promote capillary action of the material of thebonding layer 300, so a wetting agent may not be necessary for someembodiment described herein.

Upon heating, inter-metallic bonds are formed between the bonding layer300 and the upper substrate 200 and lower substrate 400 at the uppersubstrate bonding surface 202 and lower substrate bonding surface 402,respectively. The bond formed in the present embodiments between thebonding layer 300 and the upper substrate 200 and/or the lower substrate400 may be stronger than conventional bonds where no microchannels 290,490 are present. Without being bound by theory, it is believed that thebond may be stronger because of the increased surface area ofinter-metallic bonding due to the microchannels 290, 490. Additionally,depending upon the heating temperature utilized, a selected weight ratioof bonding layer 300 to upper substrate surface member 210 and lowersubstrate surface member 410 may be utilized. The weight ratio ofmaterials of the bonding layer 300 to the sum of the materials of theupper substrate surface member 210 and lower substrate surface member410 may form selected eutectics systems. For example, for a copper andtin system at about 250° C., a weight ratio of 30% copper and 70% tinmay be utilized to form a desired eutectic system. In embodiments, theweight ratio of the bonding layer 300 to the upper substrate surfacemember 210 and lower substrate surface member 410 may be about 2:8,about 3:7, about 4:6, from about 2:8 to about 4:6, or from about 2.5:7.5to about 3.5:6.5. Furthermore, it is believed that the geometry of themicrochannels 290, 490 may improve durability of the bond. As the bondis thermally cycled, sometimes above the melting point of the materialof the bonding layer 300, the eutectic system may re-form each cyclewith additional material of the upper substrate surface member 210and/or lower substrate surface member 410. The geometry of themicrochannels 290, 490 may promote formation of the eutectic systembetween the microchannels 290, 490 without reacting through the entirethickness 230 of the upper substrate surface member 210 or thickness 430of the lower substrate surface member 410.

The resulting bonded substrates are spaced by a bond distance 330, whichis the distance between the upper substrate bonding surface 202 and thelower substrate bonding surface 402. In embodiments, the bond distance330 may be from about 5 microns to about 1000 microns, from about 10microns to about 100 microns, or from about 15 microns to about 30microns.

In some embodiments, as shown in FIG. 1, the microchannels 290, 490 ofthe upper substrate 200 and the lower substrate 400 may be insubstantial alignment. However, in other embodiments, as shown in FIG.8, the microchannels 290, 490 may have complementary alignments andgeometries relative to one another.

As described herein, microchannels formed on the surfaces of substratesmay promote more secure and durable bonds between substrates.Additionally, compared to conventional bonding procedures, processingtimes may be reduced and additional wetting agents may not be necessary.The bond may be suitable for thermal cycling at relatively hightemperatures while having good thermal conductivity characteristics.

It is noted that the terms “substantially” and “about” may be utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. These terms are also utilized herein to represent thedegree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue.

While particular embodiments have been illustrated and described herein,it should be understood that various other changes and modifications maybe made without departing from the spirit and scope of the claimedsubject matter. Moreover, although various aspects of the claimedsubject matter have been described herein, such aspects need not beutilized in combination. It is therefore intended that the appendedclaims cover all such changes and modifications that are within thescope of the claimed subject matter.

What is claimed is:
 1. A system of bonded substrates, the systemcomprising: a first substrate comprising a bonding surface, wherein ageometry of the bonding surface of the first substrate comprises aplurality of microchannels; a second substrate comprising acomplementary bonding surface; a bonding layer positioned between thefirst substrate and the second substrate, wherein the bonding layerfills the microchannels of the first substrate and contactssubstantially the entire bonding surface of the first substrate, whereinthe bonding layer comprises a metal.
 2. The system of claim 1, wherein:a geometry of the complementary bonding surface of the second substratecomprises a plurality of microchannels; and the bonding layer fills themicrochannels of the complementary bonding surface of the secondsubstrate and contacts substantially the entire complementary bondingsurface of the second substrate.
 3. The system of claim 1, wherein thebonding layer comprises tin.
 4. The system of claim 1, wherein the depthof each microchannel is from about 5 microns to about 10 microns.
 5. Thesystem of claim 1, wherein the bonding surface of the first substratecomprises a metal chosen from aluminum, nickel, copper, or combinationsthereof.
 6. The system of claim *, wherein the metal of the bondingsurface of the first substrate is a direct bonded metal and themicrochannels are formed by etching.
 7. The system of claim 1, whereinat least one material of the first substrate has a melting point greaterthan a melting point of the metal of the bonding layer.
 8. The system ofclaim 1, wherein each of the microchannels of the first substratecomprise a length and a depth, the length substantially parallel withthe bonding surface of the first substrate, and wherein the ratio of thelength to the depth is at least about 10:1.
 9. A system of bondedsubstrates, the system comprising: a first substrate comprising abonding surface, wherein a geometry of the bonding surface of the firstsubstrate comprises a plurality of microchannels; a second substratecomprising a complementary bonding surface; a bonding layer positionedbetween the first substrate and the second substrate, wherein thebonding layer fills the microchannels of the first substrate andcontacts substantially the entire bonding surface of the firstsubstrate, wherein the bonding layer comprises a metal; wherein: ageometry of the complementary bonding surface of the second substratecomprises a plurality of microchannels; and the bonding layer fills themicrochannels of the complementary bonding surface of the secondsubstrate and contacts substantially the entire complementary bondingsurface of the second substrate; and the depth of each microchannel isfrom about 5 microns to about 10 microns.
 10. The system of claim 9,wherein the bonding layer comprises tin.
 11. The system of claim 9,wherein the bonding surface of the first substrate comprises a metalchosen from aluminum, nickel, copper, or combinations thereof.
 12. Thesystem of claim 11, wherein the metal of the bonding surface of thefirst substrate is a direct bonded metal and the microchannels areformed by etching.
 13. The system of claim 9, wherein at least onematerial of the first substrate has a melting point greater than amelting point of the metal of the bonding layer.
 14. The system of claim9, wherein each of the microchannels of the first substrate comprise alength and a depth, the length substantially parallel with the bondingsurface of the first substrate, and wherein the ratio of the length tothe depth is at least about 10:1.